1. Field of the Invention
The present invention relates to an olefin polymerization reactor which uses a spouted bed, to a polyolefin production system which uses a spouted bed, and to a process for producing polyolefins such as polyethylene and polypropylene using such a reactor or system.
2. Related Background Art
Olefin polymerization reactors which polymerize, within a vessel and in the presence of a catalyst, an olefin monomer fed in as a gas or liquid to form granular polyolefin particles are known to the art. However, in a single vessel, the polyolefin particles approach a completely mixed state, as a result of which there is a tendency for a short path characterized by the discharge of particles that have not grown to a sufficient size to arise or for particles that have grown too large to accumulate within the vessel.
In such cases, the formed particles have a poor structural uniformity. Other problems that tend to arise include higher catalyst costs, increased catalyst residues, and larger numbers of defects (referred to as “fish-eyes” owing to the similarity in shape to the eye of a fish) in molded articles obtained by molding multistage polymers prepared by polymerization in a plurality of reaction zones. Moreover, with complete mixing, when the polymerization of different lots is carried out by varying the polymerization conditions, because it takes time to completely discharge from the vessel the polyolefin particles that were polymerized prior to the change in conditions, a large amount of off-specification product ends up forming. One conceivable way to deal with this problem is to connect a plurality of continuously stirred reactors in series so as to create overall a plug flow pattern. However, the equipment costs associated with connecting a plurality of reactors in series are considerable.
Accordingly, there exists a desire to obtain a narrower residence time distribution and achieve plug flow in a single reactor. Known examples of such reactors include those described in Patent Publication No. 2,675,919, U.S. Pat. No. 5,235,009, and Japanese Translation of PCT Application No. 2002-537420. In addition, reactors in which particles are mixed by means of a spouted bed are also known (see, for example, Japanese Translation of PCT Application No. 2002-520426, European Patent Laid-open Publication No. 1484343, Japanese Patent Application Laid-open No. S 58-216735, Japanese Patent Application Laid-open No. S 59-42039, and Japanese Translation of PCT Application No. 2002-515516).